Advancing informed visual impact analysis and mitigation

Wind Turbine Visibility and Visual Impact Threshold Distances

Field observation of wind facilities in western landscapes revealed that the facilities were visible at distances of 36 mi (58 km) in both daytime and nighttime views, and were found a major focus of visual attention at distances of up to 12 mi (19km).

Wind Turbines near Peetz, Colorado
Wind Turbines near Peetz, Colorado

The siting of wind facilities to minimize visual impacts to high-value scenic resources presents a major challenge for land management agencies in the western United States. The visibility and potential visual contrasts associated with utility-scale wind facilities depend on complex interactions among a variety of factors. So far, however, there has been little systematic study of visibility in western landscape settings, and there is uncertainty about the distances at which wind facilities cause major, moderate, and minor visual contrasts.

Project planners at the U.S. Department of the Interior's Bureau of Land Management (BLM) found that visual impact assessments submitted for some proposed projects on BLM-administered lands analyzed potential impacts in relatively small areas around the proposed projects. The areas assessed were potentially too small, given the open landscapes, large size and scale of wind facilities, and good visibility conditions common to the western United States.

Study Summary

In a study sponsored by the BLM's Wyoming State Office, 377 observations of 5 wind facilities in Wyoming and Colorado were made under various lighting and weather conditions in three different seasons. The wind facilities ranged in size from 34 to 274 turbines and contained several models of turbines with capacities of 1.0 to 2.1 MW and blade tip heights of between 298 and 404 ft (91 and 123 m). The facilities' locations varied from elevated mesas with sky backdrops to plateaus with mountain backdrops, in near-urban, rural, and near-natural settings.

Between two and ten researchers participated in the observations. Most of the observers had some visual impact analysis experience. Facility visibility was rated on a numeric scale that was keyed to written descriptions of apparent contrast levels. Observations included several nighttime observations made as a preliminary assessment of visibility distances for aerial hazard lighting on the wind turbines.

Study Results

The facilities were found to be visible to the unaided eye at >36 mi (58 km) under optimal viewing conditions, with turbine blade movement often visible at 24 mi (39 km). Under favorable viewing conditions, the wind facilities were judged to be major foci of visual attention at up to 12 mi (19 km) and were likely to be noticed by casual observers at >23 mi (37 km). A conservative interpretation suggests that for such facilities, an appropriate radius for visual impact analyses would be 30 mi (48 km), that the facilities would be unlikely to be missed by casual observers at distances of up to 20 mi (32 km), and that the facilities could be major sources of visual contrast at distances of up to 10 mi (16 km).

Project fieldwork concluded in 2011. Study photographs and associated data are available through an online database and a Google Earth KMZ (KMZ, 35KB) file. Interim and final study results were incorporated into project reports, visual impact assessment training courses, and a publication (PDF, 1.5MB).

Please note: BLM has not adopted the recommendations of this study as guidelines for directing the development of renewable energy projects, judging the conformance of projects to VRM Class objectives, or predicting the outcomes of analyses conducted under the National Environmental Policy Act of 1969.

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